As technology has developed, mankind has vastly increased his mobility. At one time, a horse-drawn chariot was the fastest mode of surface transportation available. Today, one can travel across the surface of the earth by train at speeds in excess of 100 kilometers. As Nathaniel Hawthorne once said, "[r]ailroads . . . are positively the greatest blessing that the ages have wrought out for us. They give us wings; they annihilate the toil and dust of pilgrimage; they spiritualize travel-" The House of the Seven Gables.
Unfortunately, as the speed of trains has increased, the potential danger of operating and riding trains has also increased. The time which the operator of the train has to react to a potentially dangerous situation (such as an obstruction in the path of the train) decreases proportionally with the speed of the train. For this reason, the risk of serious accident and the occurrence of accidents increases as the speed of the vehicle increases. Likewise, nearly any accident involving a train travelling at a very high speed is likely to be a serious accident.
Many potentially dangerous situations arise on a railway. For instance, railroad tracks can be damaged by floods, landslides or sabotage. Stopped railway vehicles can obstruct the track ahead of a rapidly moving train. If the train is moving at a great speed, the train engineer often does not have sufficient time to react to a dangerous situation in order to safely stop the train in time.
Solutions to this problem have been proposed in the past. U.S. Pat. No. 3,272,982 to Stewart (issued Sept. 13, 1966) discloses a surveying system in which a satellite train car precedes a main rail car. The satellite car transmits an infrared beam to a receiver on the main rail car for the purpose of surveying the track. The satellite rail car is self-propelled, its velocity being remotely controlled via an infrared beam transmitted by the main rail car. Other references disclosing the use of satellite railway cars are U.S. Pat. No. 3,128,975 to Dan (issued April 14, 1964), Swiss Pat. No. 119,109 (issued Mar. 6, 1926) and German Pat. No. 1,234,256 (issued Feb. 16, 1967).
U.S. Pat. No. 3,258,595 to Galante (issued June 28, 1966) discloses a satellite observation body which propels itself over the surface of the water and communicates via a laser beam with a remote control station on board a submarine. The movements of the satellite body may be controlled from the remote control station. A television camera on board the satellite body surveys the surface of the water and communicates information back to the remote control station.
Several schemes have been developed for preventing collision between two train cars travelling along the same rail or for maintaining the distance between such train cars constant. See, for example, U.S. Pat. No. 3,790,780 to Helmcke et al (issued Feb. 5, 1974), U.S. Pat. No. 3,365,572 to Strauss (issued Jan. 23, 1968), U.S. Pat. No. 2,762,913 to Jepson (issued Sept. 11, 1956), and U.S. Pat. No. 3,819,932 to Auer, Jr. et al (issued June 25, 1974). Each of these schemes require cooperative transmitters and receivers mounted on each train car travelling along the railway. U.S. Pat. No. 3,934,252 to Ross et al (issued Jan. 20, 1976) discloses a radio transmitter/receiver for reliably and automatically detecting a potential collision of a protected vehicle with an arbitrary object.
U.S. Pat. No. 4,112,818 to Garehime, Jr. (issued Sept. 12, 1978) and U.S. Pat. No. 3,426,146 to Seaman (issued Feb. 4, 1969) both disclose automatic surveillance systems utilizing video cameras. See also Montgomery and Wolf, "The Surveyor Lunar Landing Television System", IEEE Spectrum, page 54-61 (August 1966).